1. Field of the Invention
The present invention relates to an image output apparatus for forming (outputting) an image on a printing medium, an image formation system including the image output apparatus and an image supply apparatus for supplying image data to the image output apparatus, an image output method, and a printed matter which is printed by the image output method. For example, the present invention relates to a textile printing system which uses a piece or roll of cloth as a printing medium and prints an image on the cloth.
2. Related Background Art
As an image output apparatus, those which perform digital image printing by using a printing head of ink jet type or thermal transfer type have spread rapidly in recent years. Generally, such an image output apparatus uses a printing head (to be referred to as a multi-head in this section) in which a plurality of printing elements are integrated, in order to increase the printing speed.
For example, as an ink jet printing head, a so-called multi-nozzle head in which a plurality of ink orifices and liquid passages are integrated is generally used. In additions in a thermal head of thermal transfer type or heat-sensitive type, it is common practice to integrate a plurality of heaters.
It is, however, difficult to uniformly manufacture printing elements of a multi-head due to, e.g., characteristic variations in the manufacture process or variations in the head constituent material. The result is a variation to a certain degree in the characteristics of the individual printing elements. As examples, a variation is brought about in the shape of orifices or liquid passages in the multi-nozzle head, and the shape or the resistance of heaters varies in the thermal head. This nonuniformity in the characteristics of the printing elements appears as nonuniformity in the size or the density of dots printed by the individual printing elements. Consequently, density unevenness takes place in a printed image.
To solve the above problem, the present applicant has proposed, in Japanese Laid-Open Patent Application No. 3-18358 and the like, an image formation apparatus in which a density unevenness reading unit is provided to periodically read the density unevenness distribution within the range of an array of printing elements, thereby reforming density unevenness correction data. In this apparatus, even if the density unevenness distribution of a head changes, the correction data is reformed in correspondence with the change. Therefore, it is possible to ensure uniform images free from unevenness at any instant.
Recently, advanced image output apparatuses have been developed in which a plurality of printing heads are provided for a printing agent of one color, and these printing heads are caused to perform either overlap printing on the same line in order to improve the print quality, or printing on different lines in order to increase the printing speed. If such an image output apparatus is for color printing, a plurality of printing heads are provided for each of printing agents of different colors.
It is an object of the present invention to provide an arrangement which performs overlap printing by using a plurality of printing heads provided for a printing agent of one color, and in which density unevenness correction can be performed efficiently for each of the printing heads.
It is another object of the present invention to perform appropriate density unevenness correction in both overlap printing and non-overlap printing.
To achieve the above objects, the present invention provides an image output apparatus which outputs an image on a printing medium by using a plurality of printing heads provided for a printing agent of one color and each having a plurality of printing elements, comprising image forming means for causing the printing heads to form a test image, reading means for reading the test image formed by the image forming means, and correcting means for performing a common correction for drive signals corresponding to the printing heads on the basis of the result read by the reading means.
The present invention also provides an image output method which outputs an image on a printing medium by using a plurality of printing heads provided for a printing agent of one color and each having a plurality of printing elements, comprising the steps of causing the printing heads to form a test image, reading the test image formed by the image forming step, and performing a common correction for drive signals corresponding to the printing heads on the basis of the result read by the reading step.
In the above apparatus or method, the test image can be one test image formed by performing overlap printing by using the printing heads.
The correction can be performed on the basis of an average value calculated by averaging density data, which is obtained by reading the test image, by the number of printing heads.
It is also possible to cause the printing heads to form their respective test images, and to separately correct the drive signals corresponding to the printing heads on the basis of individual density data obtained by reading the test images.
In this case, it is possible to time-divisionally perform the processing for separately correcting the drive signals corresponding to the printing heads.
Furthermore, the printing heads can be arranged in the conveyance direction of the printing medium to allow overlap printing or non-overlap printing on the printing medium using the printing heads. In this case, it is possible to perform the common correction when the overlap printing is to be executed, and the separate correction when the non-overlap printing is to be executed.
In the above arrangement, a plurality of such printing heads can be provided for each of printing agents of different colors.
The printing head can be an ink jet printing head which uses an ink as the printing agent and ejects the ink. This ink jet printing head can have an element for generating thermal energy, which causes film boiling in the ink, as energy to be used to eject the ink.
The above image output apparatus is applicable to a textile printing system using cloth as a printing medium.
The present invention further provides an image formation system comprising the above image output apparatus and an image supply apparatus for supplying image data relating to printing to the image output apparatus.
Another image formation system of the present invention comprises the above image output apparatus and an image supply apparatus for supplying to the image output apparatus a command for performing the overlap printing or the non-overlap printing, in addition to image data relating to printing.
Furthermore, a printed matter of the present invention is manufactured by the above method.
Also, in the present invention, this printed matter is processed to obtain a processed product. This processed product can be obtained by cutting the printed matter into a desired size and performing a step of obtaining a final processed product for each separated piece. The step of obtaining a final processed product can be sewing, and the final processed product can be clothing.
According to the present invention, one test image, for example, is formed by a plurality of printing heads provided for a printing agent of one color. Density data obtained by reading this test image is averaged by the number of heads. On the basis of this average value, a common correction is performed for drive signals for the printing heads. This makes it possible to efficiently perform the head density unevenness correction when overlap printing is to be executed by using the plurality of printing heads.
The apparatus of the present invention further comprises means for causing the plurality of printing heads to form their respective test images, and means for separately correcting drive signals for the printing heads on the basis of individual density data obtained by reading the test images. Therefore, since density unevenness correction is separately performed for the drive signals in non-overlap printing, a proper correction corresponding to the print mode is possible.